1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to the addressing of messages transmitted within a cellular telephone network.
2. Description of Related Art
Operation of a cellular telephone network to handle an incoming call dialed to a cellular subscriber mobile station is well known. Responsive to receipt at an originating (or gateway) switching node of the incoming call dialed to a mobile station, a location request (send routing) message is sent to the home location register for the dialed mobile station. The home location register then identifies a switching node currently serving the dialed mobile station. A routing request (provide roaming) message is then sent from the home location register to the serving (or visited) switching node to prepare for delivery of the call. The serving switching node then pages for the mobile station within the network. Responsive to a paging acknowledgment, the mobile station is located and the serving switching node assigns an appropriate routing number (for example, a temporary location directory number or a roaming number) for that location. The routing number is then delivered to the originating switching node via the home location register where it is used to establish a trunk call connection between the originating switching node and the serving switching node. Delivery of the call to the mobile station from the serving switching node is then accomplished by establishing a connection with a base station currently serving the mobile station. A radio frequency communications link is then established between the base station and the mobile station to carry the call connection.
The ANSI-41 (formerly IS-41) standard specifies that certain information be included within the location request and routing request messages to identify originating (or gateway) switching node. This information is needed at the serving switching node to enable the proper addressing of network messages (such as a redirection request message) that are subsequently generated by the serving switching node and addressed to the originating switching node. More specifically, a review of the ANSI-41, TIA/EIA IS-41.5-D, section 6.4.2.27, specification reveals that the location request (LOCREQ) must include a mandatory parameter identifying the originating switching node through the use of its mobile switching center identification (MSCID) for an originating MSC as specified by ANSI-41, TIA/EIA 41.5-D section 6.5.2.82. Similarly, the ANSI-41 specification indicates that the routing request (ROUTREQ) must include a mandatory parameter identifying the originating switching node through the use of its mobile switching center identification (see, TIA/EIA 415-D section 6.4.2.40).
It is recognized, however, that the mobile switching center identification (MSCID) is not the only mechanism available to identify the originating switching node. Two other known mechanisms for identifying the originating switching node within a network message are through the use of its mobile switching center identification number (MSCIN) as specified by ANSI-41, TIA/EIA 41.5-D section 6.5.2.83, or its point code subsystem number (PC-SSN) as specified by ANSI-41, TIA/EIA 41.5-D section 6.5.2.93.
With respect to the location request (LOCREQ) and routing request (ROUTREQ) messages, for example, the ANSI-41 specification indicates that these identification mechanisms may optionally be included as parameters within the messages in addition to the mandatory mobile switching center identification (MSCID). In many instances, the originating (gateway) switching node and other network nodes, such as the home location register, are programmed to include in each message as many as possible, if not all, of the available originating switching node identification mechanisms. Thus, a location request or routing request message may include all of the possible identification mechanisms, MSCID, MSCIN and PC-SSN, for the originating switching node.
Routing problems for subsequent messages originated at the serving switching node may arise when the wrong switching node addressing mechanism is included within the network message. The foregoing may be better understood by reference to several examples. First, consider the situation where the MSCID of the originating switching node is received (as is mandatory in accordance with the ANSI-41 standard). If that received MSCID is not contained within the serving switching node""s addressing database (such as may occur when the nodes are located within different national networks), then it will not be possible for that node to properly address a subsequent message (like a redirection request) using the received MSCID. Second, consider the situation where the MSCIN of the originating switching node is received (as is optional in accordance with the ANSI-41 standard). If that node does not support global title translation (GTT), then it will not be possible for the node to properly address a subsequent message (like a redirection request) using the received MSCIN. Third, consider the situation where the PC-SSN of the originating switching node is received (as is optional in accordance with the ANSI-41 standard). If that received PC-SSN is not contained within the serving switching node""s addressing database (such as when the the PC-SSN format is not the proper format for the network signaling type (S7/C7) used by the serving switching node), then it will not be possible for that node to properly address a subsequent message (like a redirection request) using the received PC-SSN. It is therefore commonplace to identify the originating switching node in a message (such as a location request message) using at least two, if not all three, of the addressing mechanisms (MSCIN, MSCID and PC-SSN).
While, generally speaking, the more addressing information that is included in the message the better the situation, the inclusion of two or more different originating switching node identification mechanisms in a single message may be problematic for the destination network node. For example, consider the situation where a serving switching node receives a routing request (ROUTREQ) message including not only the mandatory mobile switching center identification (MSCID) but also the optional mobile switching center identification number (MSCIN) and point code subsystem number (PC-SSN) for the originating (gateway) switching node. In this case, the serving switching node has three different mechanisms (each having its own benefits and drawbacks) for possible selection for use in addressing a subsequently originated message (like a redirection request). Which one should be used? The answer to this question may vary from situation to situation, in accordance with, for example the foregoing concerns over database inclusion and global title translation, and thus it is important that the serving switching node intelligently choose from amongst the available options the best addressing mechanism for the originated message.
Given access to two or more originating switching node addressing mechanisms (such as, for example, a mobile switching center identification (MSCID), a mobile switching center identification number (MSCIN) and/or a point code subsystem number (PC-SSN)), a serving switching node, when needing to address a message to that originating switching node, implements a hierarchical process for selecting one of the two or more available mechanisms for use in addressing the message. The process gives preference to use of the MSCIN, if present and if the message is being sent in an international routing context, in addressing the message. Alternatively, the process gives preference to use of the PC-SSN, if present and if the message is being sent in a national routing context, in addressing the message. Lastly, the process utilizes the MSCID in addressing the message.